Pionic and Δ (1232) degrees of freedom in nuclei

We review recent developments in the investigation of pion-like nuclear excited states. At high momentum transfers, the presently available (e,e') and (p,p') data more or less rule out the appearance of precursor phenomena indicating the proximity of a pion condensate. At low momentum transfers, the systematic quenching of Gamow-Teller and magnetic spin transitions suggests an interpretation in terms of Δ-hole screening mechanisms. Altogether, the virtual pion field in nuclei appears to be accompanied by massive repulsive correlations, while at the same time the Δ(1232) plays an important role in spinisospin excitation channels, even at low energy and momentum transfer.